As network traffic and bandwidth rapidly increase, operators have an increasingly urgent need for an intelligent grooming function of a bottom level wavelength division network, and consequently, a reconfigurable optical add/drop multiplexer (Reconfiguration Optical Add/Drop Multiplexer, “ROADM” for short) is gradually used on networks of increasingly more operators. After the ROADM is introduced to a network, an operator can quickly provide a wavelength-level service, thereby facilitating network planning and maintenance, and reducing operating expenditures and maintenance costs.
In addition, on an optical communications network for long-distance transmission, a quantity of optical-electrical-optical (Optical Electrical Optical, “OEO” for short) conversions on a system link is decreasing, and it becomes increasingly difficult to directly test a bit error rate on an electrical layer. However, testing a bit error rate on only a terminal of a link is adverse to fault locating. As transmission capacity of an optical network increases and flexibility of the optical network improves, system complexity intensifies. To effectively control and manage the optical network, it becomes increasingly important to perform optical performance monitoring (Optical Performance Monitoring, “OPM” for short) on a high-speed dense wavelength division multiplexing (Dense Wavelength Division Multiplex, “DWDM” for short) signal on the optical network.
For example, optical power monitoring can reflect a basic channel working state and guide a system to perform automatic power equalization, optical signal to noise ratio (Optical Signal to Noise Ratio, “OSNR” for short) monitoring can relatively accurately reflect signal quality, and dispersion monitoring can reflect a channel dispersion state to guide a system to perform dispersion compensation or the like on an optical layer or an electrical layer. These parameters become important content of optical performance monitoring, and facilitate damage suppression, fault locating, degradation probe, backup and recovery, and the like of an optical network, which therefore is conducive to stable working of the optical network. Therefore, optical performance monitoring needs to be performed on all important network elements on the network, and it is also necessary to perform optical performance monitoring on the ROADM.
Currently, in a solution for performing OPM on the ROADM, an external OPM module is used outside a wavelength selective switch (Wavelength Selective Switch, “WSS” for short), an optical splitter is used to split a small part from a signal of a main optical path that is in the ROADM and that needs to be monitored, and the small part is then monitored by using the OPM module. On one hand, in the OPM module, a tunable optical filter (Tunable Optical Filter, “TOF” for short) may be used to scan an optical signal to be monitored, to perform wavelength demultiplexing on a multiplexed optical signal in a time dimension. At the same time, a channel of light is extracted from the multiplexed optical signal, so that performance monitoring is performed on this channel of single-channel optical signal. On the other hand, in the OPM module, a wavelength demultiplexer (Demultiplexer) may also be used, to perform wavelength demultiplexing on a multiplexed optical signal in a space dimension. In this way, at a same output location, only one channel of signal is extracted from the multiplexed optical signal, so that performance monitoring is performed on this channel of single-channel optical signal.
In this method, an external OPM module is used to perform performance monitoring on the ROADM, and a tunable optical filter or a wavelength demultiplexer needs to be used in the OPM module, to obtain a single-wavelength optical signal by means of splitting and monitor the single-wavelength optical signal, which significantly increases a system size and system costs.